This invention relates to optical systems to produce quiescent light patterns, and to generating circles, cirrcular arcs, and approximately circular arcs that are formed by stationary optics and are steady in time for edge and groove tracking applications.
There is a need to generate small circles of light to form guiding stripes for joint location in such operations as automated welding with active torch/joint tracking. Presently, stripes are employed to locate joints which do not curve rapidly. Circles generated by a rotating prism have been used to track around corners or curves with radii smaller than about one inch. However, these circles, because they are formed from a rapidly rotating point, generate interference patterns when viewed by a television camera. Tests have shown that varying the prism rotation rate over wide ranges does not remove these patterns, merely changing their shape and motion. Therefore, a means is needed for generating quiescent circles whose radii can be conveniently adjusted. One reference on this prior art technique to trace parallel laser stripes and concentric circles on the face of a coherent fiber optic bundle by which they are transferred to a vision-guided arc welding torch and hence reimaged on the workpiece surface just ahead of the weld puddle, is commonly assigned U.S. Pat. No. 4,491,719.
Another method for generating circles, steady in time, involves focusing a beam down onto a small concentric cylindrical reflector. The Center for Welding Research at Ohio State University has described this approach in one of their member reports. The main problem with this configuration for applications within a weld torch is that the cylindrical reflector must be kept clean. Alternatively, if a coherent fiber optic bundle transfers a circular pattern to the torch, the circle projected on the bundle face must be very small (typically less than 3 mm in diameter). However, it is difficult, and thus expensive, to make small circles efficiently using a cylindrical rod reflector, because the cylinder itself must be substantially smaller than the circle, rather long and of good optical quality, and held straight in just the right place.
One or more circular prisms, also known as axicons, are employed in the present invention to generate circles and arcs. Previously, circular prisms have been employed in various applications where light dispersed about a constant polar angle must be focused to a point. One example of this is in the analysis of light passed through a Fabry-Perot interferometer.